1. Field of the Invention
The invention relates to a capacitor having a glass dielectric and to a method for the production thereof.
2. Description of Related Art
The constantly increasing need to store energy for times from microseconds to days with a large amount of electrical energy is necessitating materials having special dielectric properties.
Polypropylene film capacitors are generally used as high-power capacitors in the prior art. They can be rolled, and the dielectric—polypropylene—can be produced in the form of a very thin film. However, the dielectric breakdown voltage of approximately 1 MV/cm limits the density with which energy can be stored.
Electrolyte capacitors can also be brought to very high storage densities. For instance, Jeol in Japan has reported double-layer electrolyte capacitors with storage densities of the order of 20 Wh/l (JP 11288852 A2).
Such electrolytes, however, are in general chemically reactive and environmentally harmful, and in some cases may even be explosive.
Ceramic capacitors are furthermore known which use ceramics as dielectric, for example capacitors comprising ferroelectric phases. However, the residual porosity of ceramics limits their dielectric breakdown field strength.
Batteries, for instance lithium ion batteries, currently give the greatest storage density of up to 800 Wh/l. Batteries, however, have a limited lifetime and, in contrast to capacitors, have charging times of up to several hours.
Glasses as dielectric for capacitors are furthermore known in the prior art. Glass capacitors have been described since the 1940s. They are widely used in electronic applications for satellites and space flight, and can work in very aggressive environmental conditions. It is also known that the dielectric breakdown field strength of glasses is generally greater than that of the corresponding crystal systems. A. Hippel, R. J. Maurer, Phys. Rev., 59, 820 (1941) describe this phenomenon by comparing the breakdown field strength of quartz glass with quartz crystal. The authors indicate a breakdown field strength of the order of 7 MV/cm for quartz glass.
However, the production of capacitors from quartz glass would be an extraordinarily expensive and time-consuming process.